A loader is a construction machine typically used to transport a load of material, such as aggregate construction or mining material, from one place, such as a pile of stored material, to another, such as a truck used for hauling the material to another location. For example, a loader may be used to load a dump truck full of material or to transport material from a pile to a specific place where it is used, such as trench. Typically, loaders are wheeled or tracked vehicles having a large bucket on one end and include hydraulics or other mechanisms for raising and lowering the bucket and tilting the bucket. However, a loader can also be a stationary machine that is immobile, but used to move a load from one place to another, for example from a pile to the bed of a nearby dump truck. Generally, a loader is any device capable of using a bucket or other appropriate support structure to transport a payload from one place to another place.
Often, it is desirable to know the weight of a payload. For example, dump trucks used on the highway typically must abide by laws restricting the weight they can carry, and the restrictions are typically determined by a government highway authority. Depending on the density of the material loaded into a truck, it is possible to load more than the maximum allowed amount. In addition, loading too much weight into a truck can cause premature wear to the truck's suspension, drive train, and other parts affected by weight. In other instances, it may be desirable to know the weight of the payload. For example, when material is sold according to weight, knowing an amount of material loaded into a truck can provide a basis to calculate a cost of the loaded material.
To determine the weight of a payload, loaders often include bucket scales. A bucket scale is a system integrated into the loader which measures the weight of a payload. Typically, bucket scales measure hydraulic pressures associated with the bucket, such as pressures present in hydraulic cylinders used for lifting the bucket up and down, and for tilting the bucket about a pivot point.
Typical bucket scales require calibration before first use with a known weight by using the bucket scale to weigh the known weight and then adjusting settings of the bucket scale so that the weight registered equals the known weight. One option for calibrating a bucket scale includes use of prefabricated blocks, often cylindrical, of known weight for the purpose of calibration. Prefabricated blocks, however, are often prohibitively expensive and require maintenance. Moreover, the weight of the prefabricated blocks is unable to be distributed in the same manner as a payload of, for example, aggregate material. As a result, the use of prefabricated blocks can introduce errors into the calibration process.
Another option for calibration includes first weighing an empty loader, then weighing the same loader with a payload to determine the weight of the payload. Calibration, however, is typically performed on a job site, such as a construction or mining site, and owners of loaders often do not own the type of large scale needed to weigh loaders and, if they do, the scales generally are not located on job sites, but at other more permanent sites, such as an equipment storage facility owned by the owner of the loader.
When owners have scales on job sites, it is often for the purpose of weighing off-highway trucks. The scales used for weighing off-highway trucks are generally too small to be used for weighing the larger loaders often used for loading the off-highway trucks. Consequently, determining the weight of the payload involves weighing an empty off-highway truck, dumping a loader payload used for calibration into the off-highway truck, and weighing the off-highway truck again. Complicating matters is that larger loaders usually have buckets that are wider than the length of the beds of typical off-highway trucks. Therefore, the use of off-highway trucks with extra long beds, which are not always available, is necessary.